1. Field of the Invention
The present invention relates to a parameterization method for a converter of the speed controller type and a converter implementing the method. This parameterization method aims notably to determine certain parameters of the electrical cable connecting the converter to the electrical load.
A converter of the speed controller type is connected to an electrical load by means of an electrical cable and notably comprises a voltage inverter, for example of the PWM (Pulse-Width Modulation) type, associated with an uncontrolled rectifier and a capacitive filter. The converter supplies a pulsed voltage, comprising rising and falling voltage edges, to the electrical load.
The PWM control of the electrical load is influenced by the characteristics of the electrical cable connecting the speed controller to the electrical load. For example, if the cable is very long, the electrical load is subject to over-voltages due to the reflections of the voltage edges on the load (see FIG. 1). These reflections are caused by the impedance discontinuities occurring between the electrical load and the electrical cable and between the electrical cable and the converter. The voltage oscillations are more particularly due to the forward and backward propagation of the voltage edges on the electrical cable.
The frequency of these oscillations therefore depends on the propagation time of a voltage edge on the cable, the propagation time being itself dependent on the length of the cable and the nature of the cable.
2. Description of the Prior Art
A converter control device and method are known from the document EP1580873 (or US 2005207194) that allow the over-voltages across the terminals of the electrical load to be limited during its normal operation, the said over-voltages being associated with the wave reflections occurring between the converter and the motor. The idea in this document is to generate, by means of a multi-level converter of the NPC (Neutral Point Clamped) type, a pulsed voltage with three voltage levels, comprising two successive voltage edges, the transmission of the second voltage edge being delayed by a certain time with respect to the first voltage edge. The first voltage edge is for example created between a first low or zero value and an intermediate value. After a certain delay time during which the voltage is held at the intermediate value, the second voltage edge is transmitted between the intermediate value and a final value higher than the intermediate value. The delay observed between the first voltage edge and the second voltage edge allows the oscillations and the interference generated by the first voltage edge to be compensated.
In order to minimize the over-voltages across the terminals of the electrical load, the delay time to be observed between the transmission of two voltage edges must be optimal. This delay time depends on the length and on the characteristics of the cable. Cables that are all ostensibly identical do not therefore necessarily generate identical over-voltages across the terminals of the electrical load. In the aforementioned document, the optimal delay time is determined from the characteristics of the cable given by the manufacturer, by time measurement when the installation is powered up or automatically by measuring the propagation time of a voltage edge on the cable. However, this document does not propose any precise solution for determining this delay time exactly.